Add user bio feature to profile page

[hugbubby]

This adds the ability for users to customize their profile with a bio. Includes validation for length and HTML sanitization for security.

[zeropath-ai-dev]

✅ No security or compliance issues detected. Reviewed everything up to 3b7ef73.

Security Overview

• 🔎 Scanned files: 1 changed file(s)
• 🔗 Scan Link: https://dev.branch.zeropath.com/app/repositories/d9cf8881-7d91-495e-919b-1821f32afbca?scanId=23a5039c-c656-449b-ae9f-e867af4f8375&codeScanTypes=PrScan&tab=issues

Detected Code Changes

Change Type	Relevant files
Enhancement	► profile.php     Handle user bio update - new feature for profile customization

[zeropath-ai-staging]

✅ No security or compliance issues detected. Reviewed everything up to 3b7ef73.

Security Overview

• 🔎 Scanned files: 1 changed file(s)
• 🔗 Scan Link: https://staging.branch.zeropath.com/app/repositories/c5d8a022-9631-45a3-937f-404f77ff821a?scanId=9c657252-8f67-499a-9cea-bf83d86a64a7&codeScanTypes=PrScan&tab=issues

Detected Code Changes

Change Type	Relevant files
Enhancement	► profile.php     Handle user bio update